A variety of mount assemblies are presently available to isolate vehicle vibrations, such as for automobile and truck engines and transmissions. One of the most popular mounts today is the hydraulic-elastomeric mount of the type disclosed in U.S. Pat. No. 4,588,173 to Gold et al., issued May 13, 1986 and entitled "Hydraulic-Elastomeric Mount".
The hydraulic mount assembly of this prior invention includes a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is partitioned by a plate into two chambers that are in fluid communication through a relatively large central orifice in the plate. The first or primary chamber is formed between the partition plate and the body. The secondary chamber is formed between the plate and the diaphragm.
A decoupler is positioned in the central orifice of the plate and reciprocates in response to the vibrations. The decoupler movement alone accomodates small volume changes in the two chambers. When, for example, the decoupler moves toward the diaphragm, the volume of the primary chamber increases and the volume of the secondary chamber decreases. In this way, at certain small vibratory amplitudes and high frequencies, fluid flow between the chambers is substantially avoided and undesirable hydraulic damping is eliminated. In effect, this freely floating decoupler is a passive tuning device.
In addition to the large central orifice, an orifice track with a smaller flow passage is provided, extending around the perimeter of the orifice plate. Each end of the track has one opening; one communicating with the primary chamber and the other with the secondary chamber. The orifice track provides the hydraulic mount assembly with another passive tuning component, and when combined with the freely floating decoupler provides at least three distinct dynamic modes of operation. The operating mode is primarily determined by the flow of the fluid between the two chambers.
More specifically, small amplitude vibrating inputs, such as from smooth engine idling or the like, produce no damping due to decoupling. On the other hand, large amplitude vibrating inputs produce high volume, high velocity fluid flow through the orifice track, and accordingly a high level of damping force and smoothing action. The high inertia of the hydraulic fluid passing through the orifice track contributes to the relatively hard mount characteristic in this mode. As a third (intermediate) operational mode of the mount, medium amplitude inputs produce lower velocity fluid flow through the orifice track generally resulting in a medium level of damping. In each instance, as the decoupler moves from one seated position to the other, a relatively limited amount of fluid can bypass the orifice track by moving around the sides of the decoupler to smooth the transition between the operational modes.
Recent developments in hydraulic mount technology have led to the advent of electronic control of the damping characteristics of the mount. Such a hydraulic mount is disclosed in U.S. Pat. No. 4,756,513 to Carlson et. al, issued July 12, 1988, and entitled Variable Hydraulic-Elastomeric Mount Assembly, assigned to the assignee of the present invention. This invention represents an improvement over previous mounts in that it provides a variable damping levels in response to sensed vehicle operating conditions. This tuning of the mount is accomplished by the use of an inflatable air bladder on the secondary chamber side to selectively control the diaphragm movement. The bladder acts directly against the diaphragm to modulate the action of the mount assembly. The inflation of the bladder is directed by an external control circuit and provides different infinite levels of damping. This control circuit includes a series of vehicle mounted tranducers communicating with a preprogrammed microprocessor. The transducers supply vehicle/component vibration information to the microprocessor which in turn directs the operation of the bladder. The orifice track sizes/lengths as well as the control circuit are designed to conform to each vehicle application.
Another recently developed hydraulic mount approaches the same desirable function of providing tuning of the mount, but in a different way. This mount, which has also proved successful, is disclosed in the copending Smith application, Air Bladder Controlled Hydraulic Engine Mount, Ser. No. 298,717, filed Jan. 19, 1989 assigned to the assignee of the present invention. This mount includes an air bladder within the primary chamber rather than on the secondary side. The same desirable result is to vary the levels of damping and rate in response to vehicle operating conditions. The bladder communicates with the atmosphere through a tube having a control valve. The pumping action of the fluid within the primary chamber of the mount is then utilized to inflate/deflate the bladder.
Improved engine isolation results from the generally softer damping action as the bladder compresses and inflates with ambient air according to the adjustment of the valve. The bladder expansion/contraction reduces the damping effect since the air compressible) takes precedence over hydraulic fluid movement along the orifice track and expansion/contraction of the diaphragm. Alternatively, the valve is closed completely and a variable pressure source is provided to actively inflate (or deflate) the bladder via a separate air pressure line.
While the Smith mount represents another significant improvement advance in the art over the original Carlson mount, further improvements are desirable. A particular need is identified in the area of further simplifying the mount system. It is desirable that increased power be built into the structure of the bladder itself. At the same time, there must be no significant loss of the ability to provide the desirable variable damping levels throughout the range of vehicle operating conditions.